1. Field of the Invention
The present invention relates to an ink ribbon cassette, and more particularly to an ink ribbon cassette repeatedly usable for an extended period of time by replenishment of ink to an ink ribbon after each printing operation.
2. Description of the Related Art
According to a conventional ink ribbon cassette, an ink-absorbing member is interposed between an inner face of a wall member and an ink-storing absorbent member with the ink-absorbing member closing an opening defined in the wall member. Further, the ink-absorbing member and the ink-storing absorbent member are placed in contact with each other through entire opposing faces of the respective members including those portions of the faces corresponding to the wall opening (for example, Japanese laid-open utility model No. Hei. 4-117766).
The ink-storing absorbent member to be used in an ink ribbon cassette of the above-described type is comprised of a material capable of absorbing ink in the form of liquid, such as nonwoven fabric, fiber web, sponge or the like, and the ink-absorbing member is comprised of such material as felt. Because of this, these members, when fabricated, are apt to have size irregularity. Then, when the ink-storing absorbent member and the ink-absorbing member, if fabricated at the upper limit of their dimensional tolerances, are assembled within the wall member of a cassette casing, both of these members are set therein in a compressed state, thereby causing a portion of the ink-absorbing member to project or bulge to the outside through the opening of the wall member. This in turn increases the pressure of contact between the bulging portion of the ink-absorbing member and an ink replenishing roll, leading to inadvertent increase in the amount of ink liquid to be transferred from the ink-absorbing member to the replenishing roll for ink replenishment. More specifically, the replenishing roll will collect, by scraping, an excessive amount of ink from the ink-absorbing member; and as this excess ink is supplied to the ink ribbon and this ink ribbon is used for printing, there occurs such printing trouble as ink bleeding.
Conversely, if the ink-absorbing member and the ink-storing absorbent member are fabricated at the lower limit of their dimensional tolerances, then, when these members are assembled within the wall member of the cassette casing, there will be formed a gap between the ink-absorbing member and the ink-storing absorbent member. As a result, the contact pressure between the bulging portion of the ink-absorbing member and the replenishing roll will be reduced, thereby to decrease the amount of ink liquid supplied and transferred from the ink-absorbing member to the roll. This results in excessive decrease in the amount of ink liquid to be scraped off by the roll from the ink-absorbing member. Then, with the resultant deficiency in the amount of ink liquid to be replenished to the ink ribbon, there tends to occur a printing trouble such as blurring or obscure printing.
In view of the above-described state of the art, a primary object of the present invention is to provide an ink ribbon cassette which may restrict excessive variation in the pressure of contact between the ink-absorbing member and the replenishing roll in spite of possible presence of some dimensional tolerances in the ink-storing absorbent member and the ink-absorbing member, so that the ink may always be replenished by an appropriate amount so as to avoid the printing troubles such as ink bleeding and blurring.